Weighted bioacoustic sensor and method of using same

ABSTRACT

A sensor for sensing bioacoustic energy includes a housing comprising an interfacing portion configured to establish coupling with a body part during use. The sensor includes a transducer element coupled to the interfacing portion of the housing and configured to sense sounds produced by matter of biological origin. One or more conductors are coupled to the transducer element. A mass element is compliantly coupled to a surface of the transducer element. Intervening material is disposed between the transducer element surface and the mass element, and allows for differential motion between the transducer element surface and the mass element during excitation of the transducer element.

FIELD OF THE INVENTION

The present invention relates to medical sensing devices and, moreparticularly, to sensors and devices incorporating such sensors whoseinput is variations of bioacoustic energy and output is a conversion toanother form of energy.

BACKGROUND

A variety of devices have been developed to detect sounds produced bythe body, such as heart sounds. Known devices range from primarilymechanical devices, such as the stethoscope, to various electronicdevices, such as microphones and transducers. The stethoscope, forexample, is a fundamental tool used in the diagnosis of diseases andconditions of the cardiovascular system. It serves as the most commonlyemployed technique for diagnosis of such diseases and conditions inprimary health care and in circumstances where sophisticated medicalequipment is not available, such as remote areas.

Although many electronic stethoscopes are available on the market, theyhave yet to gain universal acceptance by the physicians and othermedical practitioners. Possible reasons for non-acceptance of electronicstethoscopes include the production of noise or artifacts that disturbthe clinician during patient evaluation, as well as limitationsassociated with amplification and reproduction of certain biologicalsounds of interest. For example, a biological sound may be present butmasked by noise, or wholly absent, and many conventional electronicstethoscopes are not capable of distinguishing between these two cases.

Noise that impacts stethoscope performance may be defined as any signalother than that of interest. Various types of noise include external orambient noise, noise related to auscultation, noise generated by theelectronic circuits of the stethoscope, and noise of biological natureproduced by the patient's body, for example.

There is a need for a bioacoustic sensor with improved sensitivity androbustness. There is a further need for such a sensor that may beincorporated in various types or medical sensing devices, such asstethoscopes, that provides for an improved signal-to-noise ratiorelative to conventional implementations. The present invention fulfillsthese and other needs.

SUMMARY OF THE INVENTION

The present invention is directed to sensors for sensing bioacousticenergy and methods for using same. According to an embodiment of thepresent invention, a bioacoustic sensor includes a housing comprising aninterfacing portion configured to establish coupling with a body partduring use. The sensor includes a transducer element coupled to theinterfacing portion of the housing and configured to sense soundsproduced by matter of biological origin. One or more conductors arecoupled to the transducer element. A mass element is compliantly coupledto a surface of the transducer element.

Intervening material is disposed between the transducer element surfaceand the mass element. The intervening material allows for differentialmotion between the transducer element surface and the mass elementduring excitation of the transducer element. The intervening materialpreferably comprises an adhesive, such as a pressure sensitive adhesive.The intervening material is capable of transmitting sound signals, andhas a low acoustic impedance.

The mass element, intervening material, and transducer element surfaceare configured to allow for mechanical deformation of the transducerelement in response to bioacoustic energy impinging on the transducerelement. Preferably, the mass element, intervening material, andtransducer element are configured to effectively amplify a signalproducible by the transducer element. Increased signal production by thetransducer element may involve reducing loss of bioacoustic energytransferred to the transducer during excitation.

The mass element may cover substantially all of an effective transducingportion of the transducer element surface. Alternatively, the masselement may cover less than all of an effective transducing portion ofthe transducer element.

The mass element may comprise a mass and a stiff sheet or membranehaving a first surface and a second surface, and the mass itself has astiff surface. The first surface of the stiff sheet or membrane may bearranged to contact the intervening material, and the mass may bedisposed adjacent the second surface.

In one implementation, a polyvinyledene fluoride-like piezoelectric film(e.g., a PVDF2 film) is encased in a polyester film as if in a pouch. Apolyester film of about 1.5 thousandths of an inch thick may be disposedon each side of the PVDF2 film, for example. In another implementation,the transducer element may comprise a laminate structure. The laminatestructure may comprise a piezoelectric film, a weight in film form, andone or more adhesive layers.

The mass element may comprise metal, non-metallic material, or compositematerial. The mass element may have a substantially uniform weightdistribution profile relative to an x-y plane of the transducer element.The mass element may alternatively have a substantially linear weightdistribution profile relative to an x-y plane of the transducer element.In other configurations, the mass element may have a substantiallynon-linear weight distribution profile relative to an x-y plane of thetransducer element. The mass element may comprise a unitary mass or aplurality of discrete mass arrangements.

The transducer element is preferably configured to modulate or generatean electrical signal in response to deformation of the transducerelement. The transducer element may comprise piezoelectric material,such as a polymeric piezoelectric film, or a piezoresistive orpiezo-ceramic material or element. The transducer element may compriseone or more strain gauges or one or more capacitive elements. Thetransducer element may be planar or non-planar, such as in the case of acurved or corrugated configuration.

The housing of the sensor may be configured for hand-held coupling to abody part during use. The sensor may include a fixing arrangementcoupled to the housing and configured to establish affixation betweenthe housing and the body part during use. For example, the sensor mayinclude an adhesion arrangement coupled to the housing and configured toestablish adhesive coupling between the housing and the body part duringuse.

One or more conductor are coupled to the transducer element, which maybe electrical conductors. In another configuration, the conductor(s)coupled to the transducer element may include at least one opticalconductor. The optical conductor may be coupled to converter circuitry.The converter circuitry may be situated remote from the sensor andconfigured to convert a received optical signal to an output electricalsignal. The converter circuitry may be coupled to one or moreelectrical-to-audio converters, such as a pair of earphones. Theconverter circuitry may be coupled to an interface configured to couplethe converter circuitry to an electronic device situated remote from thesensor.

The housing of the sensor may include a base and a cover. The base mayinclude the interfacing portion and the cover may be coupled to the basevia a compliant joint arrangement. The cover may include acousticallyabsorptive material. The interfacing portion of the housing may range instiffness from relatively pliable to substantially stiff or rigid. Theinterfacing portion of the housing may include or be formed from apolymeric material, a metal or alloy, a composite material, or a ceramicor crystalline material.

A sensor unit may be implemented that includes two or more transducerelements of a type described herein, wherein each of the transducerelements is configured to have a different frequency response. Forexample, each of the transducer elements has a stiffness, weight, shape,and thickness, and at least one of the stiffness, weight, shape, andthickness of each transducer element differing from that of othertransducer elements of the sensor. Each of the transducer elements maybe supported from the housing by a common anchoring arrangement or byseparate anchoring arrangements.

Gain control circuitry may be provided so that a gain response of eachtransducer element may be selectably adjustable. Noise cancellationcircuitry may be provided, which may include an auxiliary transducerelement disposed within the housing other than at the interfacingportion of the housing. Noise cancellation circuitry may be coupled tothe transducer element and the auxiliary transducer.

A stethoscope may be implemented to include a sensor of a type describedherein. The sensor of the may include a single transducer element or amultiplicity of transducer elements of a type described herein. A helmetmay be implemented to include one or more sensors of a type describedherein, and may include noise cancellation circuitry.

A sensor may be implemented to include communications circuitryconfigured to facilitate wired or wireless communication between thesensor and a device external of the housing. A sensor may include signalprocessing circuitry, such as a digital signal processor, coupled to thetransducer element. The signal processing circuitry may be configured tofilter and/or perform analyses on a sense signal produced by thetransducer element.

In accordance with a further embodiment, a method of sensing bioacousticenergy involves exciting a transducer in response to the bioacousticenergy. The method further involves reducing loss of the bioacousticenergy transferred to the transducer during excitation. The method alsoinvolves modulating or generating a signal by the transducer in responseto excitation of the transducer. Reducing loss of the bioacoustic energymay involve facilitating differential motion between the transducer anda stiff mass during excitation of the transducer.

Establishing coupling may involve establishing hand-held couplingbetween the interfacing portion of the sensor housing and the body part.Coupling between the interfacing portion and the body part may beestablished via adhesion or a restraining arrangement fixable to thebody.

The signal modulated or generated by the transducer may be an electricalsignal, and the method may further involve converting the electricalsignal to an optical signal and transmitting the optical signal remotelyof the sensor housing. A frequency response of the transducer elementmay be modified. Noise cancellation may be performed using thetransducer element and at least one auxiliary transducer element.Communication may be established between a device disposed within thesensor housing and a device external of the sensor housing. Variousforms of analog and/or digital signal processing and/or analyses may beperformed on the signal modulated or generated by the transducer.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a sensor that incorporates a transducer assemblythat includes a weighted transducer element in accordance with anembodiment of the present invention;

FIG. 2 is a diagram of a sensor that incorporates a transducer assemblythat includes a stiffening sheet or membrane and a weighted transducerelement in accordance with another embodiment of the present invention;

FIGS. 3A-3H show various configurations of a mass element that may becompliantly coupled to a transducer element in accordance with anembodiment of the present invention;

FIG. 4 is a diagram of a sensor that incorporates a multiplicity oftransducer assemblies, the transducer of each transducer assemblyconfigured to have a frequency response differing from other transducersof the sensor in accordance with an embodiment of the present invention;

FIG. 5A is a diagram of a sensor that incorporates a multiplicity oftransducers mounted to a common anchoring arrangement, the transducersconfigured to have a frequency response differing from other transducersof the sensor in accordance with an embodiment of the present invention;

FIG. 5B is a diagram of a sensor that incorporates a multiplicity oftransducer assemblies and a unitary mass element compliantly coupled tothe transducer element of each transducer assembly, the transducersconfigured to have a frequency response differing from other transducersof the sensor in accordance with an embodiment of the present invention;

FIG. 5C is a diagram of a sensor that incorporates a multiplicity oftransducer assemblies, a stiffening sheet or membrane, and a unitarymass element compliantly coupled to the transducer element of eachtransducer assembly, the transducers configured to have a frequencyresponse differing from other transducers of the sensor in accordancewith an embodiment of the present invention;

FIG. 6 is a diagram of a sensor that incorporates a transducer mountedin a housing, the housing including an adhesive layer that provides forintimate coupling between the housing and a body part during use inaccordance with an embodiment of the present invention;

FIG. 7 is a diagram of a sensor that incorporates a transducer mountedin a housing, the housing including an elastic fixation arrangement thatprovides for intimate coupling between the housing and a body partduring use in accordance with an embodiment of the present invention;

FIG. 8 is a diagram of a sensor that incorporates a transducer mountedin a housing, the housing shape configured for ease of hand manipulationto facilitate intimate coupling between the housing and a body partduring use in accordance with an embodiment of the present invention;

FIG. 9A shows a stethoscope that incorporates a sensor of the presentinvention;

FIG. 9B shows a helmet that incorporates a pair of sensors of thepresent invention;

FIG. 10 is a block diagram of circuitry of a sensor in accordance withan embodiment of the present invention; and

FIG. 11 is a diagram of circuitry for communicating signals produced bya sensor using optical fiber in accordance with an embodiment of thepresent invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referenceis made to the accompanying drawings that form a part hereof, and inwhich is shown by way of illustration, various embodiments in which theinvention may be practiced. It is to be understood that the embodimentsmay be utilized and structural changes may be made without departingfrom the scope of the present invention.

The present invention relates to sensors that are configured to besensitive to sounds produced by matter of biological origin and methodsfor using same. Sensors and devices incorporating such sensors includethose configured for auscultation, and may be configured to be sensitiveto sounds produced by the heart, lungs, vocal cords, or other organs ortissues of the body, for example. By way of example, a sensor of thepresent invention may be incorporated in an electronic stethoscope, ahelmet, or other externally worn or coupled apparatus or instrument thatsenses sounds produced by the body. A sensor of the present inventionmay also be configured for temporary or permanent fixation within thebody, such as a heart or lung sound monitor implanted within the body,for example.

Sensors of the present invention may be implemented to be preferentiallysensitive to a range of frequencies associated with human hearing. It isunderstood, however, that frequencies associated with body sounds belowand/or above the auditory range of frequencies may also be sensed bysensors of the present invention. For example, sensors of the presentinvention may be implemented to sense body sounds that have frequenciesranging between just above DC and about 25 kHz. Sensors of the presentinvention may produce an audible output that falls within the auditoryfrequency range, or may produce an electrical or optical sensor thatincludes content above and/or below the auditory frequency range.

Bioacoustic sensors of the present invention preferably incorporate atransducer that is configured to modulate or generate an electricalsignal in response to deformation of the transducer. Suitabletransducers are those that incorporate piezoelectric material (organicand/or inorganic piezoelectric material), piezoresistive material,strain gauges, capacitive or inductive elements, a linear variabledifferential transformer, and other materials or elements that modulateor generate an electrical signal in response to deformation. Suitablepiezo materials include polymer films, polymer foams, ceramics,composite materials or combinations thereof Additionally, the presentinvention may incorporate arrays of transducers of the same or differenttransducer type and/or different transducer materials, all of which maybe connected in series, individually, or in a multi-layered structure.

The inventors have found that a bioacoustic sensor incorporating aweighted or stiffened piezoelectric film transducer implementedaccording to the present invention, for example, provides for asignificantly improved sensitivity over conventional piezoelectric filmtransducer arrangements. The sensitivity of a weighted piezoelectricfilm transducer may be enhanced by the addition of a stiff sheet, film,or membrane disposed between the transducer element and mass. Forexample, use of a stiff sheet of sufficient mass may provide forsignificantly improved transducer sensitivity. In one experiment, sensorsensitivity was improved by more than 25 times by addition of a masscompliantly coupled to the piezoelectric film transducer element. Asuitable piezoelectric film for a bioacoustic sensor of the presentinvention include those disclosed in U.S. Pat. Nos. 4,434,114;4,365,283; and 5,889,873, which are hereby incorporated herein byreference.

Turning now to the figures, FIG. 1 illustrates a sensor 10 thatincorporates a transducer assembly 11 which includes a weightedtransducer element in accordance with an embodiment of the presentinvention. According to the embodiment of FIG. 1, a sensor 10 includes ahousing 12 to which a transducer assembly 11 is mounted. The transducerassembly 11 includes a transducer 14 which is supported by, or otherwiseconnected to, the housing 12 via anchoring arrangement 18. Thetransducer 14 includes one or more electrical contacts that allow forconnection(s) to one or more conductors 16. The conductors 16 aretypically electrical conductors or wires, but may alternatively beoptical fibers coupled to electrical-to-optical converter circuitry, asin the case of an embodiment discussed hereinbelow.

In the embodiment shown in FIG. 1, the transducer 14 is mounted to thehousing 12 so that vibrations resulting from body sounds, S_(BS),impinging on an interfacing portion 13 of the housing 12 are readilycommunicated to the transducer 14. Many mounting configurations arecontemplated that permit the transducer 14 to receive vibrationstransmitted to the transducer 14 via the interfacing portion 13 of thehousing 12.

The transducer 14 shown in FIG. 1 is affixed to the housing 12 by way ofanchoring arrangement 18. The anchoring arrangement 18 may rigidly orcompliantly couple the transducer 14 to the interfacing portion 13 ofthe housing. For example, the anchoring arrangement 18 may be an epoxy,a chemical bond, a weld or solder joint, a screw(s)/nut(s), rivet(s) orother mechanical coupling, or pressure sensitive adhesive, for example.A suitable anchoring arrangement 18 may include No. 924 Scotch AdhesiveTransfer Tape or No. DP100 Scotch Weld epoxy adhesive, both availablefrom 3M, St, Paul, Minn. It is believed that less compliant fixationarrangements should provide for better transmission of vibrations fromthe interfacing portion 13 of the housing to the transducer 14.

Further shown in FIG. 1 is a mass 19 which is compliantly coupled to thetransducer 14 by way of intervening material 21. The interveningmaterial 21 disposed between the transducer 14 and mass 19 is a materialcapable of transmitting sound signals. The intervening material 21 alsoallows for differential motion between the transducer 14 and the mass 19during excitation of the transducer 14. Allowance of differential motionbetween the mass 19 and transducer 14 allows for mechanical deformationof the transducer element 14, which is a necessary condition for thetransducing element of the transducer 14 to function properly.

The intervening material 21 may be an adhesive layer, such as a pressuresensitive adhesive layer. Other types of intervening material 21 includeNo. 732 Silicone Sealant, available from Dow Corning, Midland. Mich., orone or more layers of No. 924 Scotch Adhesive Transfer Tape, availablefrom 3M, St. Paul, Minn. The intervening material 21 may include a foammaterial, such as an open cell polyurethane low-density foam. Theintervening material 21 preferably has a low acoustic impedance.

Additionally, the mass 19 provides a relatively stiff backing to thetransducer 14. The stiff backing offered by the mass 19 enhances thetransducer's ability to generate an electric signal by vibrating orflexing, or in a compression mode, as a result of the acoustic waveenergy impinging on the housing 12. The mass 19, intervening material21, and transducer operate together to effectively amplify a signalproducible by the transducer 14.

The mass 19 may covers substantially all of an effective transducingportion of the transducer 14, as is shown in FIG. 1. Alternatively, themass 19 may cover less than all of an effective transducing portion ofthe transducer 14. The mass 19 may be formed of metal, a non-metallicmaterial such as a polymeric material, or a composite material, forexample. It is desirable that at least the surface of the mass 19 facingthe transducer 14 possess a high reflection coefficient to acousticwaves of interest and their Fourier frequency range. Generally,materials that are hard and dense, such as metals and their alloys andceramics, are suitable.

FIG. 2 is a diagram of a sensor 10 that incorporates a transducerassembly 11 in accordance with another embodiment of the presentinvention. Many of the features of sensor 10 shown in FIG. 2 areessentially those previously described with reference to FIG. 1.According to the embodiment shown in FIG. 2, the transducer assembly 11includes a stiffening layer 17, which may be in the form of a sheet,film, membrane, or other type of stiff backing structure. The stiffeninglayer 17 is disposed between the mass 19 and intervening material 21. Itis desirable that at least the surface of the stiffening layer 17 facingthe transducer 14 possess a high reflection coefficient to acousticwaves of interest and their Fourier frequency range.

The stiffening layer 17 may include an adhesive or other form offixation arrangement (e.g., mechanical coupling or weld) providedbetween the stiffening layer 17 and the mass 19. The intervening layer21 preferably provides an adhesive interface for compliantly couplingthe stiffening layer 17 to the transducer 14.

In one implementation, a polyvinyledene fluoride-like piezoelectric film14 (e.g., a PVDF2 film) is encased in a polyester film as if in a pouch.The polyester film of about 1.5 thousandths of an inch thick may bedisposed on each side of the PVDF2 film 14. In another implementation,the transducer element 14 may comprise a laminate structure. Thelaminate structure may comprise a piezoelectric film, a weight in filmform, and one or more adhesive layers.

In general, the surface area of stiffening layer 17 is preferablycoextensive with that of the transducing portion of the transducer 19.As is shown in FIG. 2, coverage of the mass 19 need not be coextensivewith the transducing portion of the transducer 19, although such aconfiguration is contemplated. It is understood that the size, shape,and/or location of mass element 19 relative to the transducer 14 maychange the frequency response and the sensitivity of transducer 14.

FIGS. 3A-3H show various configurations of mass 19. As is shown in FIGS.3A-3H, the mass 19 may have a substantially uniform weight distributionprofile relative to an x-y plane of the transducer 14. In someconfigurations, the mass 19 may have a substantially linear weightdistribution profile relative to an x-y plane of the transducer 14. Inother configurations, the mass 19 may have a non-linear weightdistribution profile relative to an x-y plane of the transducer 14. Themass 19 may be a unitary mass or comprise two or more discrete massarrangements. Many other configurations of mass 19 are contemplated, andFIGS. 3A-3H represent only some of these and are not to be regarded aslimiting.

The transducer 14 is arranged in the transducer assembly 11 (e.g., asshown in FIGS. 1 and 2) so that a region defined between the respectiveends of the transducer 14 is permitted to flex in response to forcesacting on the transducer 14. Transducer 14 preferably incorporatesmaterial or elements that transduces mechanical deformation of thetransducer 14 into a measurable electrical parameter. As was previouslydiscussed, various transducers that modulate or generate a signal inresponse to deformation may be used, such as piezoelectric orpiezoresistive material, strain gauges, capacitive or inductiveelements, or a linear variable differential transformer, among others.

For example, depending upon the configuration of transducer 14, the typeof transducing material or elements used, and the orientation and mannerof deformation of the material/elements, a useful electrical responsemay be developed at electrodes or contacts located at various regions ofthe transducer element. Electrical connections can be made to conductivepolymer, metallized foil, or conductive paint laminates or sandwichescontaining the transducing material/element, for example. Usefulmeasurable electrical parameters include a voltage, current, or a changein electrical resistance, for example.

It is known that certain semi-crystalline polymers, such as polarizedfluoropolymer polyvinylidene fluoride (PVDF), have piezoresponsiveproperties, which may include piezoelectric response. PVDF is used invarious sensors to produce a voltage as a function of force ordisplacement. Polymer resin piezoelectric materials are particularlyuseful because the polymers can be embodied as sensing elements whichare both flexible and elastic, and develop a sense signal representingresiliently biased deformation when subjected to force.

In one embodiment, transducer 14 includes a thin strip of a suitablepiezoelectric polymer as a sensing element. The sensing element oftransducer 14 is oriented within the transducer assembly 11 so that thestrip may be subject to deflection, which results in compression ortension of the sensing element in response to the applied force.Electrical contacts are made with the sensing element so that a voltagesignal is produced in response to the force. Deformation of the sensingelement of transducer 14 changes the relative positions of charges inthe polymer chain or in the semi-crystalline lattice structure, therebyproducing a voltage having an amplitude related (e.g., proportionallyrelated) to the magnitude of the sensing element deformation.

The housing 12 shown in FIGS. 1 and 2 includes an interfacing portion13. Bioacoustic signals, S_(BS), produced from within the body, forexample, are shown impinging on the interfacing portion 13. Theinterfacing portion 13 of the housing is configured to establishcoupling with a body part during use of the sensor 10. For example, theinterfacing portion 13 may be the surface of the housing 12 that comesinto contact with a patient's chest or clothing covering the chest. Thehousing 12 also includes a non-interfacing portion 15, which may be aregion of the housing 13 that faces the ambient environment during useof the sensor 10. The non-interfacing portion 15, which may be aseparable cover, may incorporate acoustically absorptive material orother vibration attenuation material or arrangement.

The transducer assembly 11 is mounted within the housing 12 so that thetransducer 14 is preferentially sensitive bioacoustic energy transmittedto the transducer 14 via the interfacing portion 13 relative to otherportions of the housing 12, such as the non-interfacing portion 15. Inthe configuration shown in FIGS. 1 and 2, for example, transducer 14 hastwo opposing major surfaces. The transducer assembly 11 is mountedwithin the housing 12 so that the major surfaces of the transducer 14are substantially parallel to the interfacing portion 13 of the housing14. Other orientations are possible depending on the particulartransducer and housing features and characteristics. Preferredorientations between the transducer 14 and interfacing portion 13 of thehousing 12 are those that provide for increased signal-to-noise ratios.

The interfacing portion 13 of the housing 12 is preferably formed from,or incorporates, material that facilitates transmission of vibrationsfrom the interfacing portion 13 to the transducer 14, such vibrationsresulting from bioacoustic energy emanating from the body and impingingon the housing 12. The interfacing portion 13 preferably has sufficientintegrity to support the transducer 14. It has been found that a widevariety of materials having varying pliability may be used, ranging fromrelatively pliable to substantially stiff

Suitable or workable materials for the interfacing portion 13 includepolymeric materials, metals including alloys, composites, crystalline orceramic materials. For example, suitable or workable materials includeviscoelastic materials, thermoplastic materials, thermosettingmaterials, paper materials (e.g., cardboard), and mineral materials(e.g., mica). Other examples include polycarbonate, styrene, ABS,polypropylene, aluminum, and other plastics and sheet metal alloys. Itis understood that this listing of materials is for illustrativepurposes only, and does not constitute an exhaustive identification ofsuitable or workable materials.

It is believed that use of relatively stiff material for the interfacingportion 13 increases the sensitivity of the transducer 14 to bioacousticsignals. It is also believed that a wide range of materials andstiffness provides for sufficient or enhanced transducer sensitivity.

A sensor 10 of the present invention may incorporate a noisecancellation arrangement by which ambient noise that could negativelyimpact sensing performance is effectively attenuated or eliminated.Sensor 10, such as that shown in FIGS. 1, 2, 4, and 5A-5C, mayincorporate an optional auxiliary transducer 6 mounted within thehousing 12. The auxiliary transducer 6 is preferably used to implement anoise cancellation methodology by the sensor 10. For example, theauxiliary transducer 6 may be mounted at a housing location thatprovides for preferential sensitivity to ambient noise. As shown in FIG.2, for example, an auxiliary transducer 6 is mounted to thenon-interfacing portion 15 (e.g., cover) of the housing 12. In thisconfiguration, auxiliary transducer 6 is preferentially sensitive tovibrations resulting from ambient noise impinging on the non-interfacingportion 15 of the housing 12. The signal modulated or produced by theauxiliary transducer 6 may be used to cancel content of the signalmodulated or produced by the transducer 14 that is attributable toambient noise.

Various known methods of effecting noise cancellation using signalsmodulated or produced by auxiliary transducer 6 and transducer 14 may beused. The auxiliary transducer 6 may of the same or similar constructionand configuration as transducer 14 or may be of a different constructionand configuration.

Performance of sensor 10 may be enhanced by addition of an arrangementconfigured to modify a frequency response of the transducer 14. Such anarrangement may be a particular shape, stiffness, weight, or thicknessof the transducer 14. Altering one or more of these parameters canmodify the frequency response of the transducer 14. In a sensorimplementation that includes multiple transducers, for example, eachtransducer may provide for a different frequency response by having atleast one of the stiffness, weight, shape, and thickness differing fromthat of other transducers of the sensor. Providing masses 19 ofdifferent weight or weight distribution may also provide for transducers14 having different frequency response.

FIGS. 4 and 5 are views of a sensor 10 that incorporate a multiplicityof transducer assemblies 11 a-11 n compliantly coupled to respectivemasses 19 a-19 n of different weight or weight distribution. Thetransducer of each transducer assembly 11 a-11 n is configured to have afrequency response differing from other transducers of the sensor 10.The transducer assemblies 11 a-11 n may be of the same or differentdesign (planar, non-planar, or mix of both or other type).

For example, a first transducer of a sensor 10 may be properly weightedto be preferentially sensitive to heart sounds, while a secondtransducer of the sensor 10 may be properly weighted to bepreferentially sensitive to lung sounds. By way of further example, afirst transducer of a sensor 10 may be properly weighted to bepreferentially sensitive to sounds associated with normal heart valveclosure activity in the frequency range 10 to 200 Hz, while a secondtransducer of the sensor 10 may be properly weighted to bepreferentially sensitive to sounds associated with abnormal heart valveclosure activity (e.g., valve stenosis) in the 10 to 700 Hz range.

As was discussed previously, the frequency response of a transducer isgoverned by several parameters, most notably the shape, stiffness,weight, and thickness of the effective transducing element of thetransducer. Altering one or more of these parameters can modify thefrequency response of the transducer. In the embodiment shown in FIG. 4,at least one of these parameters is different for each transducerassembly 11 a-11 n, resulting in each transducer of the transducerassemblies 11 a-11 n having a different frequency response. It isappreciated that other parameters can be varied among the transducerassemblies 11 a-11 n to achieve differing frequency responses.

It is appreciated that other parameters of the sensor or sensor housingcan be varied relative to the transducer assemblies 11 a-11 n in orderto achieve differing frequency responses and/or sensitivities. Thehousing 12, and more specifically the interfacing portion 13, mayinclude features that provide for a differing frequency response acrossan array of transducer assemblies 11 a-11 n. For example, the thickness,material, or other aspect of a region of the interfacing portion 13 thatsupports or otherwise influences each transducer assembly 11 a-11 n maybe varied. Elements of varying shape and material may be inserted intothe interfacing portion 13 so as to influence the frequency responseand/or sensitivity of each transducer assembly 11 a-11 n in a desiredmanner As such, differences in the frequency response and/or sensitivityof multiple transducers assemblies 11 a-11 n may be achieved at least inpart by providing for differences in the housing construction ormaterial in regions that support or influence of the transducersassemblies 11 a-11 n.

FIG. 5A is a diagram of a sensor 10 that incorporates a multiplicity oftransducer assemblies 11 a-11 n compliantly coupled to respective masses19 a-19 n mounted to a common anchoring arrangement 18. In thisillustrative embodiment, the anchoring arrangement 18 may be a stiffmaterial to which each of the transducer assemblies 11 a-11 n aremounted. This configuration may simplify manufacturing of the transducersection of the sensor 10 and installation of the transducer section intothe housing 12 during assembly.

FIGS. 5B and 5C show two illustrative configurations of a multipletransducer sensor 10 in accordance with embodiments of the presentinvention. FIG. 5B is a diagram of a sensor 10 that incorporates amultiplicity of transducer assemblies 11 a-11 n and a unitary mass 19compliantly coupled to the transducer 14 a-14 n of each transducerassembly 11 a-11 n via intervening material 21. The transducers 14 a-14n are preferably configured to have a frequency response differing fromother transducers 14 a-14 n of the sensor 10.

FIG. 5C is a diagram of a sensor 10 that incorporates a multiplicity oftransducer assemblies 11 a-11 n, a stiffening layer 21, and a unitarymass 19 compliantly coupled to the transducer 14 a-14 n of eachtransducer assembly 11 a-11 n via intervening layer 21. The transducers14 a-14 n are preferably configured to have a frequency responsediffering from other transducers 14 a-14 n of the sensor 10.

It is understood that individual transducers of a given multi-transducerassembly are preferably coupled to the sense/detection circuitry orprocessor of the sensor via individual channels, with appropriatebuffering provided for each channel. It is understood that one needs tobe careful in preventing or filtering later any cross talk that mayoccur amongst the various transducers 14 a-14 n. Although such channelsare typically defined by one or more conductors dedicated for eachtransducer, various time or frequency multiplexing techniques may beused to reduce to the complexity of the sensor's wiring scheme.

Clinicians readily appreciate that detecting relevant cardiac symptomsand forming a diagnosis based on sounds heard through a stethoscope, forexample, is a skill that can take years to acquire and refine. The taskof acoustically detecting abnormal cardiac activity is complicated bythe fact that heart sounds are often separated from one another by veryshort periods of time, and that signals characterizing cardiac disordersare often less audible than normal heart sounds.

It has been reported that the ability of medical students to recognizeheart murmurs correctly is poor. In one study, it was found that only13.5±9.8% students were able to diagnose heart murmurs correctly, andthat this does not improve with subsequent years of training bylectures, demonstration of heart sounds, and then clinical exposures. Ithas also been found, through psychoacoustic experimentation, that asound needs to be repeated from 1200-4400 times for the brain torecognize differences. Using this information, studies have beenperformed to evaluate the effect of heart sound repetition on a doctor'sability to diagnose correctly. One such study was performed with 51medical student doctors diagnosing four basic cardiac murmurs, whereeach murmur was repeated 500 times. Significant improvement (85±17.6%)of auscultatory proficiency was observed, demonstrating that repeatingthe heart sounds of interest some 500 times resulted in increasedproficiency to correctly recognize basic cardiac murmurs.

It should be appreciated that there are more than 40 different knownheart “murmur” sounds. This would make it challenging for doctors tolisten to each heart sound 500 times and remember each of the 40 knownheart sounds, as the brain has a tendency to loose the memory if thesound has not been heard for a long time.

The decline in the diagnostic skill of cardiac auscultation hascontributed to a situation for both patients and physicians to rely onalternative diagnostic methods. It has been reported that nearly 80% ofpatients referred to cardiologists have normal hearts or only benignheart murmurs. Such false positives constitute a significant waste oftime and expense for both patients and cardiologists.

A bioacoustic sensor of the present invention may be implemented to besensitive to heart sounds of varying types and characteristics. Forexample, a sensor may incorporate several transducers, each of which ispreferentially sensitive to a frequency or range of frequenciesassociated with one or a number of known heart sounds. For example,individual transducers may be “tuned” to detect particular heartmurmurs. A switching or scanning technique may be employed by which eachtransducer of an array of transducers is selectively enabled forlistening by the clinician or for output to a display/auditory device,such as by use of a wireless communication link.

In a more complex implementation, sound profiles of the 40 or more knownheart sounds may be developed (e.g., signal morphological profiles orfrequency spectrum profiles). A processor, such as a digital signalprocessor, may perform a comparison between detected heart sounds andheart sound profiles of a library of such profiles to determine presenceor absence of particular heart sounds emanating from the patient.Various algorithms, such as correlation or pattern recognitionalgorithms, may be employed to perform the comparison.

The capability of adjusting the frequency response of the bioacousticsensor 10 of the present invention advantageously allows a single sensorto have broadband sensitivity to a wide spectrum of body sounds, and theability to target body sound frequencies of particular interest.

FIG. 6 is a diagram of a sensor 10 that incorporates a transducerassembly 11 of the present invention disposed in a housing 12. Thehousing 12 includes an adhesive layer 48 that provides for intimate andsecured coupling between the sensor housing 12 and a body part duringuse. A peel-away liner 49 may cover the adhesive layer 48 and be removedprior to use of the sensor 10. The adhesive layer 48 preferably providesfor good acoustic coupling between the sensor 10 and the patient's bodypart (e.g., skin or outer clothing) For example, adhesives similar tothe pressure sensitive adhesive tapes used in the construction ofelectrocardiogram (ECG) electrodes to be adhered to skin may be used.One such tape is Micropore tape with adhesive, No. 9914, non-woven skintape, available from 3M, St. Paul, Minn. A sensor configured accordingto FIG. 6 may be particularly useful in the context of a disposablesensing device, such as a disposable stethoscope.

The housing 12 shown in FIG. 6 is a two-part housing that includes abase 40 and a cover 42. The base 42 is preferably formed of a relativelystiff material, as the base 42 incorporates an interfacing portion asdescribed hereinabove. The cover 42 may be formed from the same ordifferent material as the base 40, and attached to the base 40 using aknown coupling arrangement. A compliant interface 44 may be formedbetween the base 40 and cover 42. The compliant interface 44 is formedof a material that attenuates vibrations transmitted along or throughthe cover 42, typically produced from sources in the ambientenvironment. Also, and as previously discussed, cover 42 may be formedfrom acoustically absorptive material that aids in reducing transducerexcitation due to ambient noise. Provision of vibrationisolation/attenuation between the cover 42 and base 40 advantageouslyattenuates vibrations produced from such ambient sources (e.g., non-bodyproduced sounds), thus increasing the sensitivity of the senor 10 tobody produced sounds.

FIG. 7 is a diagram of a sensor 10 that incorporates a housing 12 havinga fixation arrangement 50. The fixation arrangement 50 facilitatesfixation of the sensor 10 to a patient's body part during use and easyremoval from the patient after use. In the embodiment shown in FIG. 7,the fixation arrangement 50 includes one or more elastic bands 54 thatare coupled to the housing 12 of the sensor 10. The elastic bands 54 areof sufficient length and elasticity to extend around the patient's bodypart of interest. The ends of the elastic bands 54 are provided with asuitable coupling arrangement that allows for secured engagement ofsensor 10 to the patient during use. In an alternative configuration,the fixation arrangement 50 may include one or more strips of adhesivetape, which may be represented by adhesive (elastic or non-elastic)bands or strips 54 in FIG. 7.

The signal processing circuitry 94 may perform more sophisticatedanalysis of bioacoustic signals received from the sensor 10, such asbody sound profile matching as discussed above. The signal processingcircuitry 94 may perform various forms of statistical analysis onsignals produced by the sensor. In such configurations, the signalprocessing circuitry 94 may include a digital signal processor.Alternatively, or in addition, an external system 114 may perform all orsome of such signal processing and analyses. The external system 114 mayinclude a display, sound system, printer, network interface, andcommunications interface configured to establish uni- or bi-directionalcommunication with the communications device 112 disposed in the mainhousing 115 of the stethoscope 90. FIG. 8 is a diagram of a sensor 10that incorporates a housing 12 having a shape configured for ease ofhand manipulation to facilitate manual coupling between the housing 12and a body part during use in accordance with an embodiment of thepresent invention. The shape of the housing 12 may be ergonomicallytailored to the specific use of the sensor. The housing 12 shown in FIG.8 may facilitate ease of hand-held manipulation of the sensor 10. Forexample, a clinician may grasp the handle projection 80 of the housing12 and apply the interfacing portion 13 of the housing to the patient'sskin or outer clothing The sensor 10 may be held in place by theclinician during the evaluation. It is understood that other housingshapes are contemplated.

FIG. 9 a shows a stethoscope that incorporates a sensor of the presentinvention. The stethoscope 90 is an electronic stethoscope configured toinclude traditional components, such as a pair of ear pieces 95 a, 95 b,ear tubes 97 a, 97 b, and a main tube 93. The main tube 93 is coupled toa main housing 115, within which a sensor 10 of a type previouslydescribed is disposed. Other components that may be disposed in the mainhousing 115 include a power source 92, signal processing circuitry 94,and a communications device 112. The signal processing circuitry 94 mayperform more sophisticated analysis of bioacoustic signals received fromthe sensor 10, such as body sound profile matching as discussed above.Alternatively, or in addition, an external system 114 may perform suchsignal processing and analyses. The external system 114 may include adisplay, sound system, printer, network interface, and communicationsinterface configured to establish uni- or bi-directional communicationwith the communications device 112 disposed in the main housing 115 ofthe stethoscope 90.

Communications device 112 may be implemented to establish a conventionalradio frequency (RF) link that is traditionally used to effectcommunications between local and remote systems as is known in the art.The communication link between communications device 112 and externalsystem 114 may be implemented using a short-range wireless communicationinterface, such as an interface conforming to a known communicationsstandard, such as a Bluetooth standard, IEEE 802 standards (e.g., IEEE802.11), or other public or proprietary wireless protocol.

FIG. 9 b shows a helmet 91 that incorporates sensors 10 a and 10 b of atype described herein. According to the embodiment shown in FIG. 9 b,sensors 10 a and 10 b may be implemented to provide enhanced hearing bythe wearer of the helmet 91, and may further provide for ambient noisecancellation such as in the manner described previously with referenceto FIG. 2. Sensors 10 a and 10 b or other sensor may be implemented toserve as a voice pick-up, the performance of which may be enhanced by anambient noise cancellation capability of a type previously described.Various devices and apparatuses that may be implemented to include oneor more sensors of the present invention are disclosed in U.S. Pat. Nos.4,756,028; 5,515,865; 5,853,005; and D433,776, which are herebyincorporated herein by reference.

FIG. 10 is a block diagram showing various components of a sensor 10 inaccordance with an embodiment of the present invention. According to theembodiment shown in FIG. 10, one or more sensors 10 of a type describedpreviously is/are coupled to an amplifier 102, typically in accordancewith a differential configuration. In an implementation that employsseveral sensors 10 or multiple transducers, each may be coupled to aseparate amplifier 102. The amplifier 102 may include a first stage thatis located on the transducer assembly, such as on or near the anchoringend of the transducer. This first amplifier stage, if needed, may serveprimarily to convert a high impedance of the transducer, such as apiezoelectric transducer, to a low, less noise susceptible impedance. Asecond stage amplifier may be used to amplify the sense signal producedat the output of the first stage.

Signal processing circuitry 104 may be coupled to the amplifier 102. Thesophistication of the signal processing circuitry 104 may vary fromsimple to complex. For example, signal processing circuitry 104 mayinclude a simple notch filter having a center frequency of 60 Hz forpurposes of attenuating noise due to common power sources. Signalprocessing circuitry 104 may include one or more bandpass filters thatenhance the sensitivity and/or signal-to-noise ratio of transducersignal content of interest.

More sophisticated filtering may be performed on the sense signal toenhance detection of particular body sounds of interest. Such filtersmay include analog and/or digital filters. Relatively sophisticatedanalog and digital signal processors may be used to provide for morecomplex signal processing, such as pattern recognition, sourceseparation, feature correlation, and noise cancellation.

A communications device 112 may be coupled to an output of the amplifier102. The communications device 112 may be of a type previously describedthat provides for a communication link between communications device 112and external system. A power source 110 provides power to the activecomponents of the sensor. A processor/controller 117 may be incorporatedto coordinate the various functions of the componentry shown in FIG. 10.Sense signals produced at the output 108 of amplifier 102 arecommunicated to downstream components via conductor(s) 106, which may beelectrical or optical conductors.

The processor/controller 117 may be configured to perform variousdiagnostic and calibration operations. For example, it may be desirableto equalize the gain response of each transducer of a given sensor. Itmay also be desirable to perform a frequency response calibration to“tune” or adjust the “tuning” of the frequency response of thetransducer(s). The gain and/or frequency response of each transducer maybe adjusted during a calibration routine so that each is at apre-established amplitude and/or exhibits a desired frequency response.Calibration may be initiated before or during use of the sensor, and maybe coordinated by the processor/controller 117. In one configuration, anexcitation source may be included with the sensor (internal or external)that generates excitation signals having known characteristics, allowingfor relatively easy and accurate calibration of transducer gain and/orfrequency response.

According to one embodiment, and as shown in FIG. 11, an impedanceconversion amplifier 118 may be implemented at or near to the transducer11 that is directly interfaced to an analog fiber optic transmitter 119.The output of the fiber optic transmitter 119 is connected to an opticalguide 116, which is connected to receiver circuitry 120. Receivercircuitry 120 includes an analog fiber optic receiver 122 that convertsthe light signal transmitted via the optical guide 116 back to anelectrical signal. The output of the optical receiver 122 is coupled tocircuitry 124 that may include additional amplification, signalprocessing and/or a system to record the signal/data communicated overthe optical guide 116. Receiver circuitry 120 may be coupled to anadditional device or circuitry 130 via electrical or wireless link 126.The additional device or circuitry 130 may be an audio output device,such as earphones, an electronic information device, such as a PDA orPC, a display device, or a network interface.

The housing in FIG. 11 that contains the piezoelectric transducer 14 maycontain a small battery to power the impedance conversion amplifier 112and optical transmitter 114, or two small wires can be included in abundle with the fiber optic guide or cable 116 for supplying power tothese and other active components.

Signal conditioning or processing circuitry can be located at, near orbe integrally associated with the transducer 11. For example, thetransducer 11 and the signal processing circuitry may be a unitarystructure. The signal conditioning or processing circuitry may includeone or more of amplification circuitry, such as buffer, gain and/orimpedance matching amplification circuitry, filter circuitry, signalconversion circuitry, and more sophisticated circuitry.

A bioacoustic sensor of the present invention provides for exceptionalsensitivity and signal-to-noise ratio by use of a transducer of the typedescribed herein and a mass that offers stiffening to the transducer.The performance of the sensor was verified using a phonocardiogram.Different heart sounds related to different diseases were regenerated interms of sound, via a compact disk, and phonocardiogram (PCS) using thissensor. There was little difference between the original sound recordedon the CD and the regenerated sensor sounds. The sensor was found to beso sensitive that it can achieve a very good signal-to-noise ratio evenwhen placed over the clothing of the patient.

The foregoing description of the various embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. For example, sleep disorders bythemselves and as indicators of more serious neurological diseases areon the rise. Sleep apnea at all ages and sudden infant death syndrome inbabies are also on the rise while their etiology is being identified. Amethod of diagnosis may involve monitoring body movements andbreath/lung sounds of patients with the above indications, which may bereadily performed using sensors of the kind described herein. Also, asensor of the present invention may be used in applications other thanbioacoustic sensing applications. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

1. A bioacoustic sensor, comprising: a housing comprising an interfacingportion configured to establish coupling with a body part during use; atransducer element coupled to the interfacing portion of the housing andconfigured to sense sounds produced by matter of biological origin, thetransducer element configured to modulate or generate a signal inresponse to deformation of the transducer element; one or moreconductors coupled to the transducer element; a mass element compliantlycoupled to a surface of the transducer element; and intervening materialdisposed between the transducer element surface and the mass element,the intervening material allowing for differential motion between thetransducer element surface and the mass element during excitation of thetransducer element.
 2. The sensor of claim 1, wherein the mass element,intervening material, and transducer element are configured to amplify asignal producible by the transducer element.
 3. The sensor of claim 1,wherein the mass element, intervening material, and transducer elementare configured to allow for mechanical deformation of the transducerelement in response to bioacoustic energy impinging on the transducerelement.
 4. The sensor of claim 1, wherein at least a surface of themass element facing the transducer element has a high reflectioncoefficient to acoustic waves.
 5. The sensor of claim 1, wherein theintervening material is capable of transmitting sound signals.
 6. Thesensor of claim 1, wherein the intervening material comprises anadhesive.
 7. The sensor of claim 1, wherein the intervening material hasa low acoustic impedance.
 8. The sensor of claim 1, wherein the masselement covers substantially all of an effective transducing portion ofthe transducer element surface.
 9. The sensor of claim 1, wherein themass element comprises a mass and a stiff sheet, film or membrane havinga first surface and a second surface, the first surface arranged tocontact the intervening material and the mass disposed adjacent thesecond surface.
 10. The sensor of claim 9, wherein at least the firstsurface of the stiff sheet, film or membrane has a high reflectioncoefficient to acoustic waves.
 11. The sensor of claim 1, wherein themass element comprises metal or non-metallic material.
 12. The sensor ofclaim 1, wherein the mass element has a substantially uniform weightdistribution profile relative to an x-y plane of the transducer element.13. The sensor of claim 1, wherein the mass element has a substantiallynon-uniform weight distribution profile relative to an x-y plane of thetransducer element.
 14. The sensor of claim 1, wherein the mass elementcomprises a plurality of discrete mass arrangements.
 15. The sensor ofclaim 1, wherein the mass element is a unitary mass element.
 16. Thesensor of claim 1, wherein the transducer element comprises a polymericpiezoelectric film.
 17. The sensor of claim 1, wherein the transducerelement comprises piezoresistive material, one or more strain gauges,one or more capacitive elements, ceramic material or crystallinematerial.
 18. The sensor of claim 1, wherein the transducer elementfurther comprises a laminate structure, the laminate structurecomprising piezoelectric film, a weight in film form, and one or moreadhesive layers.
 19. The sensor of claim 1, wherein components of thetransducer element are embedded in a mass of the intervening material.20. (canceled)
 21. The sensor of claim 1, wherein the sensor comprisesan arrangement configured to modify a frequency response of thetransducer element. 22-32. (canceled)
 33. A sensor unit comprising aplurality of the transducer elements according to claim 1, wherein eachof the plurality of transducer elements is configured to have afrequency response differing from that of at least one other transducerelement of the plurality of transducer elements.
 34. A sensor unit ofclaim 33, wherein each of the plurality of transducer elements has astiffness, weight, shape, and thickness, at least one of the stiffness,weight, shape, and thickness of each of the plurality of transducerelements differing from that of at least one other transducer element ofthe plurality of transducer elements. 35-42. (canceled)
 43. Abioacoustic sensor, comprising: a housing comprising an interfacingportion configured to establish coupling with a body part during use;means for transducing bioacoustic energy transferred via the interfacingportion of the housing to a signal; a stiffening layer; and means forfacilitating differential motion between the transducing means and thestiffening layer during excitation of the transducing means. 44-52.(canceled)